A supporting bearing is replaced with a new supporting bearing by conducting a first step and a second step. In the first step, an old inner ring before replacement is replaced with a new inner ring having an inner ring raceway diameter same as the old inner ring, and an axial length of an inner ring raceway face longer than the old inner ring so that a rolling roll is supported by this new inner ring in combination with an old outer ring and old cylindrical rollers. Thereafter, in the second step, the old cylindrical rollers are replaced with new cylindrical rollers having an axial length longer than the old cylindrical rollers, and simultaneously, the old outer ring is replaced with a new outer ring having an axial length of an outer ring raceway face longer than the old outer ring.